Settle head follow back on where you look; let the mouse reach 70 degrees

The leash only moved its reference when the head reached the leash's end,
so after turning back it sat up to the leash off, and recentring meant
overshooting with the head. The reference now eases toward the head's
facing (POINTER_LEASH_RETURN, 0.2 s) and never lags more than the leash,
so the cursor settles back to its place in the view once the head stops.
The mouse can now move the cursor up to POINTER_FOLLOW_REACH (70 degrees)
from the middle of the view, up from a fixed 40. Both are sliders on the
Pointer page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/design.md

@@ -80,7 +80,7 @@ A few overlays need special handling:
 - Just off a panel, the cursor stays on that panel's plane within `POINTER_EDGE_REACH`, so resize margins and window controls just outside the panel are reachable.
 - While the left button is held, the cursor keeps the distance it had at the press and stops re-testing collisions, so dragging past a panel's edge doesn't make it jump.
 
-Head follow is off by default. With it on (`POINTER_FOLLOW=1`, or a mouse button mapped to Head follow on/off), the cursor rides on a reference direction that's on a leash `POINTER_LEASH_DEG` from where you're facing. Turn your head within the leash and the cursor stays where it is in the room. Turn further and the reference is dragged along, and the cursor turns with it, keeping its offset. A leash of 0 makes the reference your facing direction, so the cursor is locked to your view, and mouse movement shifts it within the view. Head roll is ignored, so tilting your head doesn't swing the cursor around, and the cursor can't be pushed more than 40 degrees from the reference, so it stays in view. While the left button is held the cursor stays put in the room, so your head can't nudge a click or a drag. When you let go, it carries on from where it is instead of jumping.
+Head follow is off by default. With it on (`POINTER_FOLLOW=1`, or a mouse button mapped to Head follow on/off), the cursor rides on a reference direction that follows where you're facing, and keeps its offset from it. The reference eases toward your facing (time constant `POINTER_LEASH_RETURN`, 0.2 s), so small head movements barely move the cursor, but it never lags more than `POINTER_LEASH_DEG` behind, and once your head settles the cursor is back where it was in your view. The first version only moved the reference when your head reached the end of the leash, which left it up to the leash off after you turned back, and getting it centred again meant overshooting with your head. A leash of 0 makes the reference your facing direction, so the cursor is locked to your view, and mouse movement shifts it within the view. Head roll is ignored, so tilting your head doesn't swing the cursor around, and the mouse can move the cursor up to `POINTER_FOLLOW_REACH` (70 degrees) from the reference. While the left button is held the cursor stays put in the room, so your head can't nudge a click or a drag. When you let go, it carries on from where it is instead of jumping.
 
 Replacing a loaded driver's files, as re-running the installer used to do, leaves SteamVR honoring the virtual controller's hand role but not its laser claim: the dashboard pointer stays unassigned until SteamVR restarts. The driver installer now leaves an unchanged driver in place.
 

docs/reference.md

@@ -98,7 +98,7 @@ pointer/helper/run.sh status | log | restart
 pointer/driver/install.sh probe     # devices, hand roles, who owns the dashboard pointer
 ```
 
-The pointer settings are in `~/.config/frametop.conf`: `POINTER_SENSITIVITY`, `POINTER_IDLE`, `POINTER_WAKE_COUNTS`, `POINTER_DISTANCE`, `POINTER_CURSOR_DEG`, `POINTER_ORIGIN_FRACTION`, `POINTER_ORIGIN_MARGIN`, `POINTER_SCENE_RADIUS`, `POINTER_EDGE_REACH`, `POINTER_LASER_WIDTH`, and the head follow settings `POINTER_FOLLOW` and `POINTER_LEASH_DEG`. The example config explains each. Frametop Input Settings changes them live; after editing the file by hand, restart the relay or the helper.
+The pointer settings are in `~/.config/frametop.conf`: `POINTER_SENSITIVITY`, `POINTER_IDLE`, `POINTER_WAKE_COUNTS`, `POINTER_DISTANCE`, `POINTER_CURSOR_DEG`, `POINTER_ORIGIN_FRACTION`, `POINTER_ORIGIN_MARGIN`, `POINTER_SCENE_RADIUS`, `POINTER_EDGE_REACH`, `POINTER_LASER_WIDTH`, and the head follow settings `POINTER_FOLLOW`, `POINTER_LEASH_DEG`, `POINTER_LEASH_RETURN`, and `POINTER_FOLLOW_REACH`. The example config explains each. Frametop Input Settings changes them live; after editing the file by hand, restart the relay or the helper.
 
 ## Frametop Input Settings